Msk: Bone Infections

Front 1

what are the 3 pathways by which infection may spread to bone

Back 1

1) hematogenous
2) intro from the external environoment like via fractures or penetrating wounds (exogenous osteomyelitis)
3) direct extension from adjacent soft tissue

Front 2

three cellular responses of bone cells to infection

Back 2

1) resoprtion of infected bone by osteoclasts
2) bone formation by osteoblasts (after resorption, forms immature bone)
3) necrosis (death of osteocytes)

Front 3

what are the vascular pathways by which organisms gain access to the infx site in hematogenous osteomyelitis in childhood

Back 3

access to bone is gained via the nutrient artery and pass thru its branches to get to the metaphysis

Front 4

site within bone of the primary focus of hematogenous osteomyelitis in childhood

Back 4

the bone lined channels on the metaphyseal side of the epiphyseal plate (where the terminal vessels for the hypertrophic cartilage column travel). The channels come to a blind end and the capillary makes a 180 turn. the blood flow is sluggish when making this 180 degree turn and the channels are relatively impermeable making this a great site for bacteria

Front 5

what is sequestra

Back 5

Segments of dead bone surrounded by pus and granulation tissue

Front 6

pathogenesis of sequestra

Back 6

pus lifts periosteal sleeve away from bone --> disruption of periosteal blood supply. If the endosteal blood supply is also disrupted (via pus going into the marrow), no circ to shaft-->necrosis-->sequestra

Front 7

in hematogenous osteomyelitis, the stripping of the periosteal sleeve from the bone shaft stimulates what cellular response

Back 7

an intense osteoblastic response

Front 8

what is involucra

Back 8

a sheath of new, immautre bone that is deposited around the sequestrum in osteomyelitis

Front 9

what are cloacae

Back 9

fenestrations that form in the involucrum in osteomyelitis; its an area where the bacteria can exit and lead to a sinus tract

Front 10

three possible clinical outcomes of acute osteomyelitis;

Back 10

1) containment by host defenses
2) chronic osteomyelitits
3) sepsis and death (rare)

Front 11

complications of acute hematogenous osteomyelitis;

Back 11

seeding of other areas of the body that can lead to septicemia, pathologic fractures, infectious arthritis, draining sinuses with chronic form may develop into squamos cell carcinoma after many years

Front 12

in hematogenous osteomyelitis in kids, the periosteal sleeve is lifted off the bone by __

Back 12

pus under pressure

Front 13

pathogenesis of hematogenous osteomyelitis

Back 13

small clumps of blood borne bacteria (from URI, boil, minor skin infx) lodge in bone lined channels of the metaphyseal side of the epiphyseal plate-->thrombosis seals the channel and bacteria proliferate

Front 14

what are the most common organisms responsible for hematogeneous osteomyelitits

Back 14

staph aureus and strep pneumo

Front 15

pts with sickle cell are prone to bone infx which organism

Back 15

salmonella

Front 16

what is a common cause of hematogenous osteomyelitis in immunocompromised pts

Back 16

gram negative organisms

Front 17

T/F: when bone infx occurs in kids the distal femor or proximal tibia, the infx usually spreads to the knee

Back 17

FALSE- the infx moves away from the knee jt b/c the epiphyseal plate is firmly attached to the periosteal sleeve thus preventing the pus from extending past the growth plate

Front 18

T/F: when bone infx occurs in kids in the head of the femur, the infx usually spreads to the hip joint

Back 18

TRUE: the epiphyseal plate lies within the joint space and pus spreads from the metaphyseal focus to the jt space

Front 19

T/F: in osteomyelitis of long bones in adults, the infx is often extended into the joints

Back 19

TRUE- this is because there is no epiphyseal barrier

Front 20

draining sinuses are a feature of ___ osteomyelitis

Back 20

chronic (pus escapes from bone to soft tissues then to skin by way of sinuses)

Front 21

what are the 3 ways that the joints can become infected

Back 21

1) hematogenous seeding of the synovial membrane
2) extension from an adjacent focus of osteomyelitis
3) direct implantation via a penetrating wound or surgical procedures

Front 22

most common organisms causing infectious arthritis in children

Back 22

staph aureus

Front 23

most common organisms causing infectious arthritis in adults

Back 23

staph aureus, n gonorrhea in young sex active adults, s epidermidis is common with prosthetic jts

Front 24

microscopic changes of infectious arthritis in synovium and cartilage;

Back 24

synovial mem inflammed and thickened by PMNs and edema, after 24 hrs get necrosis of synovium then of the chondrocytes-->failure of GAGs-->deficient cartilage matrix, collagen fibers exposed

Front 25

most important laboratory studies in the diagnosis of infectious arthritis;

Back 25

WBC, ESR, CRP, joint aspirate:# white cells and glc, blood agar culture

Front 26

what white cell level in the jt is suggestive of infectious arthritis

Back 26

>50k

Front 27

what white cell level in the jt is suggestive of infectious arthritis

Back 27

<50%

Front 28

four clinical features of infectious arthritis;

Back 28

joint is swollen, warm, tender, and painful to move, also get fever and chills

Front 29

how do you txt infectious arthritis

Back 29

parenteral delivery of large concentrations of appropriate abx (use a narrow spectrum abx if only gram + cocci are found), surg drainage needed if untxt'ed for a week or more or with staph or gram neg

Front 30

three complications of infectious arthritis;

Back 30

osteomyelitis, ankylosis, dislocation, or joint destruction

Front 31

three characteristics of joint fluid in infectious arthritis;

Back 31

increased amt, PMNs, death of chondrocytes

Front 32

radiographic findings of osteomyelitis

Back 32

early: mottled bone at metaphyseal area from destructive and resorptive changes, later areas of involucrum and sequestra

Front 33

what do sequestra look like on xray

Back 33

opaque areas of bone surrounded by areas of radiolucency from pus and granulation tissue

Front 34

___ can demonstrate acute osteomyelitis at an early stage

Back 34

Radioisotope scanning using technetium phosphate or gallium compounds (note: b/c decreased bld supply it may result in a false negative)

Front 35

clinical course of acute hematogenous osteomyelitis

Back 35

starts with fever and other signs of systemic infx, pain and swelling in the area, localized tenderness in metaphyseal area that later extends along the shaft

Front 36

which bones are most commonly affected by hematogenous osteomyelitis and why

Back 36

distal and proximal femur, proximal tibia and proximal humerus because they are near the most rapidly growing epiphyses

Front 37

which bones can you get septic arthritis from hemat osteomyelitis in kid

Back 37

proximal femur, distal fibula, proximal humerus and radial neck because intra articular physis

Front 38

what are some features of chronic osteomyelitis

Back 38

drainage of pus from skin, hard to eradicate, may last for years, may have periods of quiescence and activation

Front 39

what is a brodie abscess

Back 39

bone abscess from past osteomyelitis that was contained by host defenses

Front 40

is hematogenous osteomyelitis seen more in kids or adults

Back 40

kids

Front 41

what site is usually involved in the adult form of hematogenous osteomyelitis

Back 41

vertebral bodies,

Front 42

what is the etiology of hemat osteomyelitis in adults

Back 42

usually s/p GU or gyn surg from seeding of pelvic plexus of veins to vertebra, also seen with IVDA

Front 43

how can you distinguish btwn infx and tumor of vertebra on xray

Back 43

infx usually involves the IV discs

Front 44

txt for bone infx

Back 44

specific and bacteriacidal abx early and in high doses, if abx not enough- drain abscesses and remove sequestra

Front 45

what is the most common cause of exogenous osteomyelitis

Back 45

open (compound) fractures

Front 46

what are two differences in the pathophys of exogenous vs hematogenous osteomyelitis

Back 46

in exogenous the infx usually remains localized and goes quickly from acute to chronic phase

Front 47

can you rule out osteomyelitis with a negative xray

Back 47

no! it takes about two week to see the bony changes on xrays and need to have lost 30-40% of bone

Front 48

infectious arthritis is commonly seen in which joints

Back 48

rapidly growing hips and knees

Front 49

is surg txt more impt in the early phase with osteomyelitis of infectious arthritis

Back 49

infectious arthritis